It is true in more than just theory. While it is true that some men may be determined to stray, in most cases of marital infidelity the man (or woman as the case may be) is trying to fulfill an emotional need that is not being met in the home.

He paid attention to me.

She seemed to appreciate the things I did for her.

He made me feel beautiful/valuable/cherished.

I just needed to be with someone who treated me like a man.

He listened to me.

She respected me.

So, I still maintain that if the wife is giving the husband the attention he needs in the home, he won't be trying to get it from somewhere else.